1. The Field of the Invention
This application relates generally to drill bits and methods of making and using such drill bits. In particular, this application relates to sonic drill bits that are used to collect a core sample, as wells as methods for making and using such sonic drill bits.
2. The Relevant Technology
Often, drilling processes are used to retrieve a sample of a desired material from below the surface of the earth. In a conventional drilling process, an open-faced drill bit is attached to the bottom or leading edge of a core barrel. The core barrel is attached to a drill string, which is a series of threaded and coupled drill rods that are assembled section by section as the core barrel moves deeper into the formation. The core barrel is rotated and/or pushed into the desired sub-surface formation to obtain a sample of the desired material (often called a core sample). Once the sample is obtained, the core barrel containing the core sample is retrieved. The core sample can then be removed from the core barrel.
An outer casing with a larger diameter than the core barrel can be used to maintain an open borehole. Like the core barrel, the casing can include an open-faced drill bit that is connected to a drill string, but both with a wider diameter than the core barrel. The outer casing is advanced and removed in the same manner as the core barrel by tripping the sections of the drill rod in and out of the borehole.
In a wireline drilling process, a core barrel can be lowered into an outer casing and then locked in place at a desired position. The outer casing can have a drill bit connected to a drill string and is advanced into the formation. Thereafter, the core barrel and the casing advance into the formation, thereby forcing a core sample into the core barrel. When the core sample is obtained, the core barrel is retrieved using a wireline system, the core sample is removed, and the core barrel is lowered back into the casing using the wireline system.
As the core barrel advances, the material at and ahead of the bit face is displaced. This displaced material will take the path of the least resistance, which can cause the displaced material to enter the core barrel. The displaced material can cause disturbed, elongated, compacted, and in some cases, heated core samples. In addition, the displaced material is often pushed outward into the formation, which can cause compaction of the formation and alter the formation's undisturbed state.
Further, the displaced material can also enter the annular space between the outer casing and the borehole wall, causing increased friction and heat as well as causing the casing to bind and become stuck in the borehole. When the casing binds or sticks, the drilling process is slowed, or even stopped, because of the need to pull the casing and ream and clean out the borehole.
As well, bound or stuck casings may also require the use of water, mud or air to remove the excess material and free up the outer casing. The addition of the fluid can also cause sample disturbance and contamination of the borehole.
Additional difficulties can arise when drilling hard and/or dry formations. In particular, while drilling hard and/or dry formations, the displaced material can be difficult to displace. As a result, the material is often re-drilled numerous times creating heat, inefficiencies, and stuck casings.